Typical electric water heaters are constructed with one or two electric-powered heating elements to heat water in the water tank, depending on the size and utilization of the water heater. Each element utilizes an electromechanical thermostat mounted onto the side of the tank at the point where the screw cap of the element connects to the side of the water tank. There are a number of disadvantages associated with such constructions.
Current electromechanical thermostats use bimetal technology for actuation of a set of contacts that either energize or deenergize the heating element. Such bimetal technology is comparatively imprecise and the response time to temperature changes in the water tank are relatively slow, thereby reducing water heater efficiency.
Another significant problem with present construction is the difficulty of protecting against "dry fired" elements. "Dry fire" occurs when power is applied to a heating element without water surrounding the element. Such dry firing rapidly causes damage to the heating element, thereby sharply reducing its useful life span. In most instances, dry firing can cause immediate failure of the element.
Current electromechanical thermostats also utilize a comparatively large and bulky thermostat bracket and occupy a comparatively large amount of surface area on the side of the water tank. This reduces energy efficiency since polyurethane foam insulation that surrounds the remainder of the tank is not used in this space. This occurs because the chemicals that form the polyurethane foam can interfere with the electromechanical thermostat controls during assembly and field service. Current methods for preventing such interference include foaming aprons, fiberglass batts or EPS foam dams, all of which have lower thermal efficiency (K-factors) than the polyurethane foam surrounding the remainder of the tank.
All of the above constructions result in a large number of manufacturing parts and steps, all of which add to the final cost of the product.